The embodiments of the present application relate to the technical field of wireless communications, and in particular to a method, system and device for triggering and performing spectrum sensing, used for solving the problem in the prior art that if the sensing period is set too long, a decline of service quality between an authorization system and a cognitive system or even a network paralysis will be caused due to interference; and if the sensing period is set too short, an increase in power consumption of devices and a waste of spectrum resources will be caused. The method for performing spectrum sensing in the embodiments of the present application includes: a sensing node judging whether or not the channel quality has declined to the requirement for performing in-band spectrum sensing; and after determining that the channel quality has declined to the requirement for performing in-band spectrum sensing, the sensing node performing in-band spectrum sensing. By way of applying the embodiments of the present application, the problems of decline of service quality between an authorization system and a cognitive system or even a network paralysis due to interference caused by setting the sensing period too long, or an increase in power consumption of devices and a waste of spectrum resources caused by setting period too short, can be avoided.